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April 28th, 1930.
Dr. Louis Schwartz,
Surgeon, U.S.P.H.S.,
Room 505 Broadway,
New York City.
Dear Sir:
Mr. Lee has handed me your letter of April 24th, request-
ing information relative to the composition of Undark.
Undark consists of & mixture of a specially prepared
crystaline zinc sulphide, containing minute amounts of copper,
manganese and cadmium, and radioactive salts in the form of radium,
mesothorium or a. mixture of the two. For the past three or four
years the only radioactive material used has been radium. Prior
to that time we used either radium alone or a mixture of radium
and mesothorium. The amount of radioactive material used, expressed
in terms of micrograms of radium element per gram of zine sulphide,
may vary from seven to thirty in the grades of material most widely
and commonly used.
Under separate cover we are sending you one gram of our
grade "L" Undark.
Very truly yours,
Vice President.
HHBarker:RH
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"ocrText": "April 28th, 1930.\nDr. Louis Schwartz,\nSurgeon, U.S.P.H.S.,\nRoom 505 Broadway,\nNew York City.\nDear Sir:\nMr. Lee has handed me your letter of April 24th, request-\ning information relative to the composition of Undark.\nUndark consists of & mixture of a specially prepared\ncrystaline zinc sulphide, containing minute amounts of copper,\nmanganese and cadmium, and radioactive salts in the form of radium,\nmesothorium or a. mixture of the two. For the past three or four\nyears the only radioactive material used has been radium. Prior\nto that time we used either radium alone or a mixture of radium\nand mesothorium. The amount of radioactive material used, expressed\nin terms of micrograms of radium element per gram of zine sulphide,\nmay vary from seven to thirty in the grades of material most widely\nand commonly used.\nUnder separate cover we are sending you one gram of our\ngrade \"L\" Undark.\nVery truly yours,\nVice President.\nHHBarker:RH"
}